There is a difference between ‘the supervisor had no contact’ and ‘there were no opportunities for DS to contact the supervisor’.
At the end of the day, a dissertation isn’t about meeting the course requirements. It’s about producing an original and novel piece of work - in other disciplines it would be about conducting your own piece of research, something completely new. It’s the pinnacle of the students’ course.
You haven’t mentioned what mark your DS got, but you don’t seem to imply he failed. He admitted himself that he didn’t put as much effort in as he could have on the synopsis. If you ask yourself honestly, do you think the work he put in deserves a higher grade? Not the hours put in, not based on what he’s got in other modules, but did he really put in the level of work to achieve a high grade dissertation? Reading around the subject, researching, bringing in different elements of things he has learnt. The lack of push on his part to resolve the issues (3 emails for something he can’t access doesn’t seem a huge amount) makes me wonder how he approached the dissertation.
That said, to some extent posters (including me) have largely ignored your actual question.
I assume a step 1 form is the first part of lodging a complaint. If he’s asked to make a complaint I assume that would therefore be the logical next step.
A complaint is unlikely to lead to his grade being raised based purely on the complaint being upheld. An appeal is more likely to do that. The university should have the process clearly laid out in policies and protocols (May be called a code of practice) on their website which should lay out the steps and the possible outcomes.